Method of fabricating heat exchangers



Nov. 28, 1967 T. F. PAULS 3,354,532

METHOD OF FABRICATING HEAT EXCHANGERS Filed May 27, 1965 4 Sheets-Sheet l FIG-l INVENTOR. THE/FUN FPAULS A T TORNE V Nov. 28, 1967 T. F. PAULS 3,354,532

METHOD OF FABRICATING HEAT EXCHANGERS Filed May 27, 1965 4 Sheets-Sheet 2 FIG-4 INVENTOR. THE/QO/VFPAULS A 7' TORNEY Nov. 28, 1967 T. F. PAULS 3,354,532

METHOD OF FABRICATING HEAT EXCHANGERS Filed May 27, 1965 4 Sheets-Sheet 5 INVENTOR. 7' HERON F PAULS kZm/g W ATTORNEY Nov. 28, 1967 T. F. PAULS 3,354,532

METHOD OF FABRICATING HEAT EXCHANGERS Filed May 27, 1965 4 Sheets-Sheet 4 i 6 ii J H H E! H r INVENTOR. 4% 4% y THERONFPAULS A TTORNE) United States Patent 3,354,532 METHOD OF FABRICATING HEAT EXCHANGERS Theron F. Pants, Godfrey, Ill., assignor to Olin Mathieson Chemical Corporation, a corporation of Virginia Filed May 27, 1965, Ser. No. 459,221 2 Claims. ((31. 29157.3)

This application is a continuation-in-part of my copending application Ser. No. 287,240, filed June 12, 1963, now US. Patent No. 3,273,227.

This invention relates generally to the fabrication of heat exchange devices and more particularly to the fabrication of single piece sheet metal heat exchange structures having secondary heat dissipating fins integrated therewith.

A commonly used and eflicient type of heat exchange unit for evaporators, air conditioning, condensers, internal combustion engine cooling radiators and the like is formed from a plurality of superimposed sheets of metal having internally disposed between the sheets a number of conduits generally in a parallel spaced arrangement extending from a first or intake header to a second or outlet header. One or more of such units may be employed; the conduits or tubes serve to carry a heat exchange medium such as water or other coolant in conductive relationship with another medium such as air or other gas passing between the tubes. This type of construction is typical of automobile radiators where, for example, the heated water issues from the cooling block of the engine with the aid of a pump, first enters one of the two headers, and then passes through a great number of thin-walled, relatively fiat, closely spaced tubes between which cooling air is blown and which extend usually vertically from one to the other of the headers. Condensers are also frequently of this same type of construction.

According to one known method of manufacture as illustrated in US. Patent 2,690,002, this type of heat exchange unit may be readily manufactured to provide a great multiplicity of tubes in a sheet of metal. This method involves the application of a suitable predetermined pattern of weld-inhibiting material between component sheets, pressure welding all adjoining areas eX-' cept those separated by the weld-inhibiting material, thereby forming a unified composite panel, and inflating along the unwelded areas to erect the tubes integral with the resultant tubed panel. Full advantage heretofore has not been taken of this method inasmuch as the tubes formed are of rather flat or oval shape with the major dimensions lying within or parallel to the panel in which the tubes are formed. In many applications it is desirable that the tubes extend not only longitudinally but also extend perpendicularly out of the panel to a considerable extent so as to place a greaternumber of the tubes in spaced parallel relationship rather than a lesser number in the same plane. This design adapts the units to fabrication as single pieces of large size, a lesser number of which may then be put together for installations where the external medium passes through perforations in the panel transversely to it rather than passing parallel to the panel along its surfaces.

In accordance with the concepts of this invention, a sheet metal panel is formed according to the procedure of the above-mentioned US. Patent 2,690,002, to form the desired tubular passageway system in its embryonic 3,354,532 Patented Nov. 28, 1967 form. This panel is then slit along a plurality of parallel spaced-apart lines extending between two oppositely disposed headers to define the interconnecting tubes. The areas of the panel lying between adjacent slits are then bent or twisted out of the normal plane of the panel so as to dispose such areas in substantially perpendicular relationship to the plane of the panel, and are then swaged, for reasons to become evident. The tubular passageway system is then inflated to form the desired tubes.

In order to improve the heat transfer characteristics of the device, secondary heat dissipating fin material may i be inserted between the parallel opposing surfaces or rolls the device is fabricated so of adjacent tubes and secured in place as by brazing or soldering. This construction, while extremely simple to fabricate and assemble, presents a practical and highly efiicient heat exchanger adapted to provide a maximum amount of external heat exchange medium flow between the tubes with a minimum amount of turbulence or impediment thereto.

Having thus generally described the invention, it becomes a principal object thereof to provide a method of producing an efiicient heat exchange device adapted for transfer of heat between an internal and external heat exchange medium.

Another object of the present invention is to provide a method of producing a heat exchange device having a plurality of parallel heat transfer tubes interconnected between a pair of headers for maximum flow of an internal heat transfer medium.

Still another object of the present invention is to provide a method of producing a heat transfer device having a plurality of heat transfer tubes interconnected between a pair of headers, the tubes being elongate in cross-section with the cross-sectional major dimension of the tube being disposed at substantially right angles to the normal plane of the panel from which the device is fabricated.

Still another object of the present invention is to provide a method of producing a heat exchange device having a plurality of heat transfer tubes interconnected between a pair of oppositely disposed headers which are bent or twisted out of the normal planeof the panel from which as to provide slots or apertures through which an external heat transfer medium may flow unimpeded over the external surfaces of the heat transfer tubes.

between a pair of headers and having the major cros's-' sectional dimension disposed at substantially right angles to the normal plane of the panel from which the device is fabricated to provide elongate apertures in which secondary heat dissipating fin stock material is inserted in heat transfer relationship with the outer walls of the tubes to achieve maximum efiiciency of heat exchange between the internal and external heat transfer mediums.

Still another object of the present invention is to provide a' method of producing a device of the character in a minimum number of steps of simplified nature.

Further objects and advantages of the present invention will become apparent from the following detailed description when considered in conjunction with the accompanying drawings, in which:

FIGURE 1 is a plan view of one embodiment of the completed heat exchange device of this invention;

FIGURE 2 is a composite plan view illustrating a num 3 ber of steps involved in the fabrication of the device of FIGURE 1;

FIGURE 3 is a sectional view taken on line 3--3 of FIGURE 2;

FIGURE 4 is a view similar to FIGURE 3 illustrating the device in an intermediate stage of fabrication;

FIGURE 5 is a fragmentary cross-sectional view of the device of FIGURE 2 in an intermediate stage of the fabrication;

FIGURES 6 and 7 are cross-sectional views similar to FIGURE 5 illustrating subsequent stages in the fabrication;

FIGURE 8 is a cross-sectional view similar to FIGURE 5 illustrating a portion of the completed device of FIG- URE 1 and taken along the lines 88 thereof; and

FIGURE 9 is a further cross-sectional view of the cornpleted device of FIGURE 1 taken along the lines 99 thereof.

Referring now to the drawings and particularly to FIG- URE 1, there is seen an illustrative embodiment of this invention which is a heat exchange device generally indicated by the reference numeral 10. The initial stage of fabrication of this device is substantially as set forth in great detail in the above-mentioned US. Patent 2,690,002, and is generally illustrated, in conjunction with other steps in the formation of the heat exchange device 10, in FIG- URES 2, 3 and 4.

Referring now to FIGURES 2 and 3, it will be seen that the heat exchange device 10 is initially formed from a plurality of superposed fiat metal sheets 12 and 14. Sheet 12 has applied thereto a pattern of weld-preventing material 16 which is a foreshortened version of the desired pattern of tubular passageways in the finished article. This pattern consists of a pair of parallel bands 18 and 20 which are spaced apart adjacent a pair of opposite edges of the stack of sheets formed by the individual sheets 12 and 14. Interconnecting the two bands 18 and 20 are a plurality of bands 22 of weld-preventing material which cover the extent of sheet 12 intermediate bands 18 and 20 except for elongated parallel islands 24 which are free of weld-preventing material, and which also extend between the aforementioned bands 18 and 20. It will become apparent that the bands 18 and 20 of weld-preventing material correspond to the headers in the finished article and that the bands 22 correspond to the plurality of interconnecting tubes. In order to provide ingress and egress apertures for a heat transfer medium, the bands 18 and 20 may be extended to an edge of sheet 12 as indicated at 26. It will also be seen that a marginal portion of sheet 12 along opposite sides transverse to the aforementioned opposite sides has been left free of weldpreventing material 16 forming a peripheral marginal area 28 with the exception of the two strips 26 extending to one of the transverse edges for the ultimate provision of openings adapted for connection to an external source of heat transfer medium.

The stack of component sheets 12 and 14 with weldpreventing material 16 sandwiched therebetween is then temporarily secured together as by clamps, spot welding or the like to prevent relative movement between the sheets 12 and 14. The assembly thus formed is then heated to a required temperature and fed through a pair of pressure rolls which exert sufiicient pressure on the stack to firmly weld the sheets 12 and 14 together into a single integrated sheet in the areas not coated with the weldpreventing material 16. Simultaneously with the bonding operation the sheets 12 and 14 undergo a substantial reduction in thickness as well as an elongation in the direction of rolling whereby the foreshortened pattern of weldpreventing material is stretched to a length corresponding to the desired pattern of tubular passageways in the finished article. FIGURE 4 illustrates in cross-section the unified sheet 30 with the unwelded portions 32 at this stage of the fabrication.

Referring again to FIGURE Wi b? 3 t a Bl r rality of slits 34 are formed in the islands 24 free of weld-preventing material, the slits extending almost the full length of these islands. Two additional slits 36 are provided in the transverse marginal area free of weldpreventing material for a purpose hereinafter to become apparent. The slits 34 and 36 may be formed during any desirable stage of the fabrication process, either in the individual sheets 12 and 14, or after the sandwich of sheets 12 and 14 and Weld-preventing material 16 has been formed and temporarily secured together or still alternatively after the aforementioned hot rolling step. Preferably the last-mentioned alternative would be selected so as to eliminate both the problem of proper alignment of individual sheets 12 and 14 with slits already formed therein, and the problem of rewelding of adjacent slit edges during the hot rolling step if no Weldpreventing material is inserted between these edges. However, it is apparent that the article is readily adaptable to any of a number of arrangements of the aforementioned steps to achieve the heat exchange device in its embryonic form as illustrated in cross-section in FIGURE 4.

As can be seen in FIGURE 5, the areas of the com posite slits 34 and 36 are then rotated or twisted out of the normal plane of the sheet 30 so as to dispose the major cross-sectional dimension of such areas at ap proximately right angles to the normal plane of sheet 30. The areas 38' between adjacent slits 34 correspond to the tubes 38 before inflation thereof, and the areas between the two outermost slits 34 and the slits 36 correspond to two solid portions 66 and 68, see also FIG- URE 1. The rotation of these areas is accomplished by any desirable means, and is of an extent covering sub stantially all of the length of the slits 34 and 36 previously formed in the unified sheet 30. Of course, when bending the portions of the sheets 30 between the slits, it is desirable to maintain the transition portions 56, which lie between the point of connection between the headers 40 and 42 and the remainder of the tubes 38 which are disposed in the aforementioned perpendicularrelationship, as short as possible within the limits of the bending characteristic of the metal in order to provide the maximum length of the resulting apertures 54 for flow of air through the apertures.

These areas 38' are then exposed to a plurality of tools to swage these areas, thereby increasing the major cross sectional dimensions thereof, for reasons to become readily apparent. A variety of tools may be used in such a swaging operation. Those illustrated in FIGURES 5-7 comprise a plurality of retaining bars 70 which may be inserted through the apertures 54, as by being introduced into alternate apertures 54 from opposite sides of the panel in the directions of the arrows 70' seen in FIG- URE 5. As can be seen more clearly in FIGURE 6, the tools 70 may be inserted completely through the apertures 54 such that confronting side faces of the tools 70 constitute restraining platens for the subsequent swaging operation. For this purpose, each of the tools 70 may include two steps 71 for purposes to become evident.

Referring now to FIGURE 7 of the drawings, it will be seen that when the tubes 70 are in place a force may be applied to push the tools 70 more closely together, thus swaging the areas 38 as well as the strips 66 and 68. This force may be applied in any desired manner, as by forcing the outer retaining strips 66 and 68 interiorly toward each other. The pressure caused by the motion of the tools 70 causes the metal of the areas 33' and strips 66 and 68 to flow, resulting in the desired swaging. An example of the swaging obtained in one test is that the major cross-sectional dimension was increased from 0.5"

.to 1.5, while the minor cross-sectional dimension was decreased from 0.030" to 0.010". It will be evident that the steps 71 may form end stops for the swaging of the areas 38'.

' Following the swaging operation, the tools 70 may be removed. The unwelded areas 26 which extend to the transverse edge of the unified sheet30, see FIGURE 2, may then be mechanically pried open and a suitable nozzle inserted therein and connected to an external source of fluid pressure. All unwelded areas of the panel 30, including of course the areas 38', may then be inflated by introduction of a fluid under pressure to yield the tubes 38, as illustrated in FIGURE 8. This expansion may take place unrestrained, or if so desired, spacer bars may be inserted into the apertures 54 to limit the expansion of the tubes 38. It will be noted that when the tubes 38 are inflated, the welded portions of sheets 12 and 14 formerly defined by the islands 24 free of weld-preventing material now constitute oppositely directed flanges 60, thereby leaving the opposing faces 52 of tubes 38 smooth and free of any projecting obstructions. These flanges constitute additional heat transfer stock and in addition add structural rigidity to the device and reinforce the leading edge of the tubes for minimizing dimension thereof.

Following the expansion of the tubes 38, fin stock 58 may be inserted into the apertures 54 between adjacent tubes 38, and fin stock 62 and 64 inserted into the apertures between the outermost tubes 38 and retaining strips 66 and 68 respectively. The fin stock 58, 62, 64 may take the form of closely corrugated or pleated fin stock, as illustrated in FIGURE 1. After insertion, the fin stock may be secured in place, as by brazing, soldering, or the like.

The tools 70 illustrated in the drawings are merely exemplary. For example, it is also possible to employ a tapered tool which is inserted in a Wedging fashion to swage the areas 38 as the tool progresses laterally through the apertures 54. It is also possible to employ a tool having one side flat and one side tapered so that a combination wedging and slitting operation is performed. Introduction of such tools laterally into the apertures would yield a sliding operation on one side of each of the areas 38' and a wedging operation on the opposite side.

Referring again to FIGURE 1, it will be seen that upon completion of the above steps the heat exchange device comprises the integrated sheet 30 of generally ract-angular configuration, having the parallel spaced-apart internally disposed headers 40 and 42 and the elongate tubular passageways 38. The headers 40 and 42 terminate adjacent an edge of sheet 30 in inlet and outlet openings 44 and 46 respectively, to which conduits 48 and 50 respectively are connected for communication of the heat exchange device with a source of internal heat transfer medium. Furthermore, it will be seen that an external heat transfer medium can flow over the fin stock 58, 62, and 64 secured within the relatively wide and elongate slots or apertures 54, thus materially increasing the available heat exchange area of the device. Communication between the headers 40 and 42 and the interconnecting tubes 38 is maintained through the interior of the tubes 38 which traverses the transition portion 56 of tubes 38. Moreover, the above procedure yields the desired differential in wall thickness between the headers and tubes, with the headers having a wall thickness approximately three times that of the wall thickness of the tubes. Accordingly, greater heat transfer contact area between the tubes and the external heat exchange medium is achieved, while at the same time maintaining a higher degree of structural rigidity in the header portions of the device and greater support for the tubes therebetween.

It should be noted that with any of the above embodiments and alternate methods of fabrication, as much cooling capacity as required may be achieve-d by arranging the heat exchange units in multiples with the headers of the several units being connected in parallel.

It will be apparent from the foregoing description and accompanying drawings that there has been provided a heat exchange device and method for making the same which is believed to provide a solution to the foregoing problems and achieve the aforementioned objects. It is to be understood that the invention is not limited to the illustrations described and shown herein which are deemed to be merely illustrative of the best modes of carrying out the invention, and which are susceptible of modification of form, size, arrangement of parts, and detail of operation, but rather is intended to encompass all such modifications as are Within the spirit and scope of the invention as set forth in the appended claims.

What I claim and desire to secure by Letters Patent is:

1. A method of fabricating a heat exchange device from a composite sheet formed of two superposed planar sheets having a pattern of weld-preventing material interposed between said sheets, said pattern including a pair of parallel spaced-apart bands located adjacent opposite edges of said composite sheet and extending to a transverse edge of said sheet and a plurality of closely spacedapart bands lying parallel to said transverse edge and joined at opposite ends with said pair of bands, said pair of bands and plurality of bands thereby defining islands free of said weld-preventing material, said method comprising the steps of (A) slitting said composite sheet in said weld-preventing material free islands over a major portion of the length thereof to provide a plurality of individual strips of said composite sheet,

(B) bending said strips adjacent the opposite end portions thereof in a rotary direction relative to the longitudinal axis of said strips by approximately to displace the elongate portion of said strips between said end portions out of the normal plane of said composite sheet, thereby forming elongate apertures between adjacent confronting surfaces of said strips,

(C) swaging said strips to increase the major crosssectional dimensions thereof while decreasing the minor cross-sectional dimensions thereof, and

(D) expanding said pattern of weld-preventing material by applying thereto a fluid under pressure to completely expand the areas of said composite sheet covered with said weld-preventing material.

2. A method of producing a heat exchange device from a composite sheet formed of two superposed planar sheets having a pattern of weld-preventing material interposed between said sheets, said pattern including a pair of parallel spaced-apart first bands located adjacent opposite edges of said composite sheet and extending to a transverse edge of said sheet and a plurality of closely spaced-apart second bands lying parallel to said transverse edge and joined at opposite ends with said pair of first bands, said pair of first bands and plurality of closely spaced-apart second bands lying parallel to said transverse edge and joined at opposite ends with said pair of first bands, said pair of first bands and plurality of second bands thereby defining islands free of said weld-preventing material, said method comprising the steps of (A) slitting said composite sheet in said weld-preventing material free islands over a major portion of the length thereof to provide a plurality of individual strips of said composite sheet,

(B) rotating said strips over a major portion of the length thereof by approximately 90 to dispose the major cross-sectional dimensions of said strips in a plane substantially perpendicular to the plane of said composite sheet,

(C) swaging said strips to increase the major crosssectional dimensions thereof,

(D) forming a system of inflated hollow tubes in said composite sheet corresponding to said pattern of weld-preventing material by applying thereto a fluid at a first pressure to expand the areas of said composite sheet covered with said weld-preventing material, said system of partially inflated hollow tubes comprising (1) a pair of first tubes corresponding to said pair of first bands, and

(2) a plurality of second tubes corresponding to said plurality of second bands, and

(E) inserting secondary heat exchange fin stock be- 2,991,047 tween adjacent confronting surfaces of said second 2,999,304 tubes. 2,999,308

3,089,225 References Cited 5 UNITED STATES PATENTS 2,690,002 9/1954 Grenell 29-157.3 2,932,491 4/1960 Miller 29-1573 8 Bailys 29-1573 Pauls 29157.3 Pauls 29-1573 Hever 29157.3

JOHN F. CAMPBELL, Primary Examiner.

P. M. COHEN, Assistant Examiner. 

1. A METHOD OF FABRICATING A HEAT EXCHANGE DEVICE FROM A COMPOSITE SHEET FORMED OF TWO SUPERPOSED PLANAR SHEETS HAVING A PATTERN OF WELD-PREVENTING MATERIAL INTERPOSED BETWEEN SAID SHEETS, SAID PATTERN INCLUDING A PAIR OF PARALLEL SPACED-APART BANDS LOCATED ADJACENT OPPOSITE EDGES OF SAID COMPOSITE SHEET AND EXTENDING TO A TRANSVERSE EDGE OF SAID SHEET AND A PLURALITY OF CLOSELY SPACEDAPART BANDS LYING PARALLEL TO SAID TRANSVERSE EDGE AND JOINED AT OPPOSITE ENDS WITH SAID PAIR OF BANDS, SAID PAIR OF BANDS AND PLURALITY OF BANDS THEREBY DEFINING ISLANDS FREE OF SAID WELD-PREVENTING MATERIAL, SAID METHOD COMPRISING THE STEPS OF (A) SLITTING SAID COMPOSITE SHEET IN SAID WELD-PREVENTING MATERIAL FREE ISLANDS OVER A MAJOR PORTION OF THE LENGTH THEREOF TO PROVIDE A PLURALITY OF INDIVIDUAL STRIPS OF SAID COMPOSITE SHEET, (B) BENDING SAID STRIPS ADJACENT THE OPPOSITE END PORTIONS THEREOF IN A ROTARY DIRECTION RELATIVE TO THE LONGITUDINAL AXIS OF SAID STRIPS BY APPROXIMATELY 90* TO DISPLACE THE ELONGATE PORTION OF SAID STRIPS BETWEEN SAID END PORTIONS OUT OF THE NORMAL PLANE OF SAID COMPOSITE SHEET, THEREBY FORMING ELONGATE APERATURES BETWEEN ADJACENT CONFRONTING SURFACES OF SAID STRIPS, 